A. Field of the Invention
The present invention relates to a flywheel assembly, and particularly a flywheel assembly provided with a damper mechanism between first and second flywheels.
B. Description of the Background Art
A flywheel is attached to a rear end of a crank shaft of an engine for dampening nonuniform crank shaft rotation during low-speed driving. The flywheel carries a ring gear for a starter and also includes means to support a clutch mechanism.
Such a flywheel assembly has been known where a flywheel is divided into first and second flywheels, and a damper mechanism is arranged between them. The damper mechanism includes elastic members which are arranged between the first and second flywheels, and are circumferentially compressed when the first and second flywheels rotate relative to each other. Some types of damper mechanisms include a friction generating mechanism which operates in parallel with the elastic members for dampening vibrations.
In the foregoing flywheel assembly, a power transmitting system can be divided into input and output sides with the elastic member of the damper mechanism therebetween. In such a system the moment of inertia of the input side and output side define a resonance frequency whereby, at a corresponding rotation speed of the engine, natural vibration occurs in the flywheel assembly. Ideally, the resonance frequency should be at a speed well below the idling speed of the engine.
In the flywheel assembly, the rotation speed of the engine passes through the resonance frequency, for example, in a speed range lower than 500 rpm when the engine starts or stops. At this time, an excessively large variation in torque may occur such that the damper mechanism may be damaged and undesirable noises and/or vibrations may occur. Under such conditions, an excessively large torque variation produce impact on the damper mechanism that may exceed a limit or stop torque of the damper mechanism.
In order to overcome the above problem, the damper mechanism may be formed a viscous resistance generating mechanism which utilizes a viscosity of fluid to generate a large resistance against an excessively large torque variation. Also, a lock mechanism may be used that locks the first and second flywheels together during at speeds close to the resonance frequency. The lock mechanism would also release the two flywheels from each other in a high-speed ranges.
Generally, the above described damper mechanism is arranged axially between the first and second flywheels. In a repair operation where a worn damper mechanism is replaced by a new damper mechanism, it is necessary to remove the second flywheel. However, removal of the second flywheel complicates the repair operation.